1. Field of the Invention
The present invention relates to the field of optics and, more particularly, to spectrometric devices of the type incorporating a multiplex or Fellget advantage. Still more specifically, the invention pertains to a spectrophotometer using an array of radiation emitting elements configured for activation in Hadamard encodement or Fourier frequency encodement patterns.
2. Description of the Prior Art
Recent prior art regarding spectrometric devices of the type incorporating a multiplex or Fellget advantage have focused primarily upon various "masking" devices that implement the Hadamard multiplex advantage. The book "Hadamard Transform Optics" by Martin Harwit, et al., published by Academic Press in 1979, provides an excellent overview of the applied mathematical theory and the degree to which common optical components are used in Hadamard spectroscopy and imaging applications. Fateley U.S. Pat. No. 4,799,795, hereby incorporated by reference, discloses an electronically alterable vanadium dioxide crystalline mask interposed in an optical pathway between a light source and a detector. This mask has a matrix of optical cells activated by a computer linkage to form various Hadamard encodement patterns which consist of spatially arranged sets of cells in either opaque or transparent modes. Electronically operable masks present a distinct advantage over mechanically operated masks which are subject to misalignment, jamming, and lack of scan repeatability.
While the electronically alterable masks provided a significant advance in the state of the art, problems still remain. First, the cell components of the electronically alterable mask each contribute their own band of absorption to the spectra for analysis, which fact may detrimentally affect detector count readings within critical spectral regions of interest. Second, components within the cells may polymerize when they are exposed to certain spectral regions of light such as ultraviolet light, which circumstance renders the mask inoperable. Finally, although the crystalline mask operates more quickly than did the various prior mechanical mask devices, the individual cells of the crystalline mask still require a transition relaxation time to pass between the opaque and transparent modes. This relaxation time requirement and related delays may, under some operational demands, become a limiting factor in spectroscopic analysis.
Laser spectroscopy provides distinct advantages over conventional non-laser spectrophotometers in certain fields including absorption spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and long range (e.g., atmospheric) spectroscopy. The advantageous laser characteristics include enhanced brightness, enhanced spectral purity, directionality, and the ability to produce light in extremely short pulses. Unlike the early laser amplifier materials that typically fluoresced light over a very narrow spectral region, modern materials, and particularly the organic laser dyes, are capable of fluorescing light in a relatively broad spectral range. This characteristic allows individual lasers to be tuned for output to different narrow spectral ranges by adjusting the angle at which laser light strikes a monochromator. The output can be further tuned for an extremely narrow frequency by additionally incorporating such devices as a Fabry-Perot etalon, which are also adjustable at different angles. An overview of this type of tuning apparatus particularly regarding dye lasers exists in the book "Topics in Applied Physics", Dye Lasers, Vol. 1, edited by F. P. Schafer, pp. 38-39, 69, 131, 190-193, published by Springer-Verlag in 1973, but similar apparatus is known in the art.